linux-kernel - Re: [RFC PATCH RESEND v2 2/2] selftests/memfd: Add tests for F_SEAL_FUTURE

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Message-ID: <6f24a4ad-613f-46f4-ad33-31ca21c383c7@lucifer.local>
Date: Wed, 8 Jan 2025 21:06:10 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: "Isaac J. Manjarres" <isaacmanjarres@...gle.com>
Cc: Jeff Layton <jlayton@...nel.org>, Chuck Lever <chuck.lever@...cle.com>,
        Alexander Aring <alex.aring@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, surenb@...gle.com,
        kaleshsingh@...gle.com, jstultz@...gle.com, aliceryhl@...gle.com,
        jeffxu@...gle.com, kees@...nel.org, kernel-team@...roid.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH RESEND v2 2/2] selftests/memfd: Add tests for
 F_SEAL_FUTURE_EXEC

On Thu, Jan 02, 2025 at 03:32:51PM -0800, Isaac J. Manjarres wrote:
> Add tests to ensure that F_SEAL_FUTURE_EXEC behaves as expected.
>
> Signed-off-by: Isaac J. Manjarres <isaacmanjarres@...gle.com>

This looks reasonable,

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  tools/testing/selftests/memfd/memfd_test.c | 79 ++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
>
> diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
> index c0c53451a16d..abc213a5ce99 100644
> --- a/tools/testing/selftests/memfd/memfd_test.c
> +++ b/tools/testing/selftests/memfd/memfd_test.c
> @@ -31,6 +31,7 @@
>  #define STACK_SIZE 65536
>
>  #define F_SEAL_EXEC	0x0020
> +#define F_SEAL_FUTURE_EXEC	0x0040
>
>  #define F_WX_SEALS (F_SEAL_SHRINK | \
>  		    F_SEAL_GROW | \
> @@ -318,6 +319,37 @@ static void *mfd_assert_mmap_private(int fd)
>  	return p;
>  }
>
> +static void *mfd_fail_mmap_exec(int fd)
> +{
> +	void *p;
> +
> +	p = mmap(NULL,
> +		 mfd_def_size,
> +		 PROT_EXEC,
> +		 MAP_SHARED,
> +		 fd,
> +		 0);
> +	if (p != MAP_FAILED) {
> +		printf("mmap() didn't fail as expected\n");
> +		abort();
> +	}
> +
> +	return p;
> +}
> +
> +static void mfd_fail_mprotect_exec(void *p)
> +{
> +	int ret;
> +
> +	ret = mprotect(p,
> +		       mfd_def_size,
> +		       PROT_EXEC);
> +	if (!ret) {
> +		printf("mprotect didn't fail as expected\n");
> +		abort();
> +	}
> +}
> +
>  static int mfd_assert_open(int fd, int flags, mode_t mode)
>  {
>  	char buf[512];
> @@ -998,6 +1030,52 @@ static void test_seal_future_write(void)
>  	close(fd);
>  }
>
> +/*
> + * Test SEAL_FUTURE_EXEC_MAPPING
> + * Test whether SEAL_FUTURE_EXEC_MAPPING actually prevents executable mappings.
> + */
> +static void test_seal_future_exec_mapping(void)
> +{
> +	int fd;
> +	void *p;
> +
> +
> +	printf("%s SEAL-FUTURE-EXEC-MAPPING\n", memfd_str);
> +
> +	fd = mfd_assert_new("kern_memfd_seal_future_exec_mapping",
> +			    mfd_def_size,
> +			    MFD_CLOEXEC | MFD_ALLOW_SEALING);
> +
> +	/*
> +	 * PROT_READ | PROT_WRITE mappings create VMAs with VM_MAYEXEC set.
> +	 * However, F_SEAL_FUTURE_EXEC applies to subsequent mappings,
> +	 * so it should still succeed even if this mapping is active when the
> +	 * seal is applied.
> +	 */
> +	p = mfd_assert_mmap_shared(fd);
> +
> +	mfd_assert_has_seals(fd, 0);
> +
> +	mfd_assert_add_seals(fd, F_SEAL_FUTURE_EXEC);
> +	mfd_assert_has_seals(fd, F_SEAL_FUTURE_EXEC);
> +
> +	mfd_fail_mmap_exec(fd);
> +
> +	munmap(p, mfd_def_size);
> +
> +	/* Ensure that new mappings without PROT_EXEC work. */
> +	p = mfd_assert_mmap_shared(fd);
> +
> +	/*
> +	 * Ensure that mappings created after the seal was applied cannot be
> +	 * made executable via mprotect().
> +	 */
> +	mfd_fail_mprotect_exec(p);
> +
> +	munmap(p, mfd_def_size);
> +	close(fd);
> +}
> +
>  static void test_seal_write_map_read_shared(void)
>  {
>  	int fd;
> @@ -1639,6 +1717,7 @@ int main(int argc, char **argv)
>  	test_seal_shrink();
>  	test_seal_grow();
>  	test_seal_resize();
> +	test_seal_future_exec_mapping();
>
>  	if (pid_ns_supported()) {
>  		test_sysctl_simple();
> --
> 2.47.1.613.gc27f4b7a9f-goog
>